DD257362A3 - ARRANGEMENT FOR DETERMINING DATA CHARACTERIZING THE CRYSTALLIZATION PROCESS AND / OR MEASUREMENT SIZES - Google Patents

Abstract

The invention relates to an arrangement for determining the crystallization process characterizing data and / or Messgroessen in the Kristallzichting from melting with moving seed crystal with the aim of objectifying and automating the crystallization process as far as possible. The task is, in particular in the Hochtemperaturkristallzighigation, to increase the life of thermally stressed parts of the breeding apparatus and Impfkeimstange and process-related, evaluable data for scattering and control of the crystallization process to obtain. The object is achieved in an arrangement with rotating and axially movable pulling spindle with a seed rod holder carrying a Impfkeimstange solved by the fact that radiation receivers and transmitters, radiation-conducting optical elements, aperture and filter arrangements are provided in Keimstangenhalter or the drawing spindle. The monocrystalline Impfkeimstange has a radiation-absorbing and selective radiation-conducting doping zone. There are additional detectors are provided, the other, the crystallization process characterizing parameters, eg. For example, measure the weight of the growing crystal. Measured values obtained simultaneously via different measuring channels are fed to evaluation circuits whose output signals bring about the actuation of the control devices of the crystal growing system. Fig. 1

Description

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Field of application of the invention

The invention relates to an arrangement for determining data characterizing the crystallization process and / or measured variables in plants for the growth of single crystals of melts, melt solutions and solutions, preferably in the Hochtemperaturzüchtung, with moving seed crystal.

Characteristic of the known technical solutions

Taking into account the material-specific properties of physical and chemical compounds, various crystal growth methods and devices have been developed for their monocrystalline representation. So z. B. for the growth of single crystals from a melt of the Kyropoulos process (used essentially at working temperatures below 1000 ⁰ C) and the Czochralski process (generally for crystallization temperatures above 1000 ⁰ C usual) known in which a substantially the same Material as the single crystal to be grown existing seed crystal is placed in a, located in a heated crucible, slightly overheated melt. The seed crystal is attached to the pulling spindle of the growing apparatus, usually with the aid of a seed holder, crystallographically oriented and is rotated by the rotating pulling spindle. In this case, an uncomplicated, accurate, easily detachable and mechanically gentle attachment of the most frequently usable seed crystal on the front side of the pulling spindle of the breeding apparatus of great importance. At the same time the joint must ensure the stable, reproducible and crystallographically accurately oriented attachment of the seed crystal, regardless of the speed of the pulling spindle and the working temperature. The simultaneous fulfillment of all these requirements is not achieved by the hitherto practiced variants of seed crystal design and attachment, especially in the Hochtemperaturzüchtung, in a satisfactory manner. In addition, a targeted use of the optical and certain other properties of the seed crystal used to determine the crystallization process characterizing evaluable readings and their use for the rational optimization of breeding technology is not yet known.

In the widespread Czochralski method, the rotating seed crystal is additionally drawn out of the melt in the direction of the drawing spindle axis after the melting process has taken place in coordination with the advancing crystal growth. Crucible and pulling spindle with attached seed crystal are in a breeding atmosphere, which prevails in the interior of a usually hermetically sealed against the outside atmosphere container of the crystal growing device (recipient). Instead of a melt, certain monocrystals can also be grown from a melt solution or solution according to this principle. It is for the successful breeding of high quality crystals, especially those intended for use as active or passive optical components or semiconductors / microelectronics single crystals, according to the above methods of melting, melting solutions or solutions in addition to meeting the usual equipment requirements and consideration Material-specific features as a procedural requirement increasingly the use of suitable automatic control and regulation methods for monitoring and targeted influencing the crystallization process over at least one closed loop commanded. For reasons of growth-kinetic and control engineering, it is desirable to obtain as early as possible relevant information about the actual state of the crystallization zone (region immediately before the phase boundary between the growing crystal and the liquid phase), e.g. on the temperature of the melt and its spatial distribution, the shape of the crystal growth front (interface), the shape of the meniscus forming around the crystal and the instantaneous mass growth rate (mass crystallizing per unit time) and their tendency to form suitable manipulated variables on the basis of this information and thus to be able to control and regulate the course of the crystallization process. It is known that temporal changes in the shape and position of the growth front are accompanied by local fluctuations in the mass growth rate ("Kristallografija" 24 [1979], vyp. 1, pp. 192-194) and usually cause a deterioration of the real structure are in turn the result of temperature fluctuations of the liquid phase near the crystallization front, the latter eventually reflecting more or

less severe disturbances of the thermodynamic equilibrium in the energy balance of vonstatten going in the crystallization of thermal energy transfer and mass transport processes and their complex interactions and are practically never completely avoid. Consequently, for the reasons mentioned, automation of the breeding process which serves to improve the crystal perfection must necessarily be aimed at stabilizing the growth front during the entire growing period. In terms of an optimal stabilization of the crystallization process, it would therefore be desirable, for reasons of control engineering, to determine the current temperature conditions in each case in the diffusion layer in front of the crystallization front or in its immediate surroundings. In practice, however, this encounters considerable difficulties and, therefore, the values of secondary technological parameters which disadvantageously reflect the actual course of the crystallization process only with restrictions are determined in the known stabilization methods and their variants.

The subsequent characteristic of the known technical solutions describes known types of seed crystal attachment in the growth of single crystals of melts, melting solutions and solutions with moving seed crystal as well as in these breeding methods conventional stabilization methods for automatic control and regulation of the growth process.

According to the prior art, the attachment of the seed crystal to the pulling spindle of the crystal growing apparatus by adhering to a carrier with "heat-resistant Kitten" (water glass) or by mortaring in acting as an intermediate ceramic tube with high temperature mortar ("Methods of Crystal Growth", VEB Deutscher Verlag of the Sciences, Berlin 1973, p. 582). Another method consists in wrapping the seed crystal with precious metal wires of platinum, iridium, rhodium or the like heat-resistant materials ("Journal of Applied Physics" 36 [1965], p 1741, "Journal of Crystal Growth" 12 [1972] 120, "Journal of Crystal Growth" 15 [1972], p 157) Also, the suspension on a platinum wire has already been proposed (DT-OS 2442517) .A further known fastening variant consists in the squeezing of a tube made of precious metal at the end of the drawing spindle after the seed crystal has been inserted ("Journal of Crystal Growth" 15 [1972], p. 188; "Methods of Crystal Growth", VEB Deutscher Verlag der Wissenschaften, Berlin 1973, p. 582) Technique according to the attachment of the seed crystal is used in wrapped with noble metal wire, thin-walled tubes ("Journal of Applied Physics" 33 [1962], p.3064; "Journal of Crystal Growth" 3.4 [1968], p. 295; Journal of Crystal Growth "10 [1971], 133, "Platinum Metals Review" [1973], p. 46). In some cases, the tube is laterally slotted to increase the effectiveness of the wire wrapping.

Among the disadvantages of these types of attachment is that the attachment of the seed crystal is associated with relatively complicated manual operations that require a high degree of skill of the operator.

The exact orientation of the seed crystal is problematic and z.T. not possible with the required quality and reproducibility. When clamping by means of wire or clamping in pipes a considerable mechanical stress of the seed crystal can not be excluded due to different thermal expansion coefficients. In practice, this often leads to breakage and thus to the loss of the seed crystal, including the already grown single crystal.

When glued or mortared seed crystals, there is a risk of self-loosening during breeding, especially when working with very high melting point compounds, where the binder is no longer solid enough and in a possible dripping makes the entire melt unusable by contamination. In particular, in difficult to grow and expensive material consist of types of crystals in which the repeated use of the seed crystal is particularly desirable, this represents a serious economic loss or technical setback. The frequent applicability of the fastening wires and tubes used is in the Practice often not given because they are - especially at high operating temperatures - after a few uses become brittle (eg iridium) or welded together and thus unusable.

Affected by the same shortcomings is also the seed crystal attachment in pipes by means of clamping screws (DWP 27705, "Journal of Physics" 84 [1933], p 677, "Review of Scientific Instruments" 9 [1938], p 322-324; "Einkristalle", Springer-Verlag Berlin-Goettingen-Heidelberg-Munich 1962, p.276 / 277, Fig. 190; "Methods of Crystal Growth", VEB German Publishing of Science, Berlin 1973, pp. 563 and 582; "Solid State Technology ", January 1974, pp. 52-55) or sticks (" Journal of Crystal Growth "41 [1977], p.262-274, Fig. 5).

According to a more advanced state of the art, the proposed crystal fixtures based on the chuck principle (ZS-PS 3446603; "Kristallografija" 4 [1959], p.261; "Improved Techniques for Growth of Single Crystals Suitable for Laser Applications, Arthur D. Little, Inc. Acorn Park, Cambridge, Mass., USA, Dec. 1965, pp. 1-37, Fig. 2, "Review of Scientific Instruments" 37 [1966], p.1094; DT -AS 1245317; "Methods of crystal growth", VEB German publishing house of the sciences, Berlin 1973, p.564imd 582). However, this type of attachment of the seed crystal also has the disadvantage that the latter usually has a different thermal expansion coefficient from the metals used for the chuck. In order to prevent slipping out of the seed crystal from the seed holder at high operating temperatures, therefore, the seed crystal in the cold state, d. H. be attached at the beginning of the breeding process, under considerable clamping effect in the germ holder. In addition, all the seed crystal fasteners described so far is the procedural deficiency own that it caused by the unforeseen solidification of the melt during the breeding process, z. B. by disturbances in the power grid or sudden defects of the crystal growing apparatus through which in such cases further rotating pulling spindle for shearing or breakage of rigidly connected to it and stuck in the solidified melt / melt solution seed crystal comes. To overcome these disadvantages, a non-clamping molybdenum seed holder is already known, which consists of a hollow shaft with conical inner profile and lateral slot for suspending a seed crystal ("Journal of Crystal Growth" 22 [1974], p 65) For a universal applicability of this principle, it is disadvantageous that, for a precise orientation of the suspended seed crystal, it is necessary to work a conical orientation surface at its upper end, which is associated with additional technical outlay This potential instability of the fastening calls into question the exact and reproducible orientation of the seed crystal and, in turn, can only be detrimental because of the disadvantage of higher speeds of the pulling spindle and, with repeated use of the seed crystal, swinging oscillations of the seed crystal he increased mechanical stress, z. B. by inserting a spring or laying a weight can be corrected.

Furthermore, in the crystal growing the bayonet joints widely used in the art have been used, but only for connecting two parts of the pulling spindle of a crystal growing apparatus and not for the actual attachment of the seed crystal to the pulling spindle ("Rostkristallov" 1 [1956], p 262; Nature "(London) 181 [1958], S.4603;" Crystal Breeding ", VEB German publishing house of the sciences, Berlin 1963, P. 286).

An advanced seed crystal holder (DD-PS 193516) consists of a according to the bayonet principle on a arranged between seed crystal and pull rod germ holder rod, both sides open sleeve made of high temperature resistant precious metal with a melt facing, inwardly beaded edge as a support surface for a inserted into the sleeve, Slotted ring disc made of high-temperature-resistant precious metal. From this slotted annular disc of the seed crystal in an annular, in him exactly parallel to his as. Orientation surface serving upper end surface extending groove clamped and tension-free to be worn. In addition to ensuring a crystallographically accurate and reproducible oriented, stable position of the seed crystal regardless of the speed of the pulling spindle and the working temperature of this crystal holder to allow easy Aüswechselbarkeit of the seed crystal and at the same time act in terms of a slip clutch between the seed crystal and germ support rod. However, in the production of single crystals from the melt with moving seed crystal, especially in high-temperature cultivation, the use advantages sought with this seed crystal holder are not practically effective, because the junction between the seed crystal and the seed holder rod used during the growing process of a very strong thermal Exposure is exposed. This leads z. B. to Verschweißerscheinungen between the metallic parts of said seed crystal holder, so that its components after completion of the breeding process often can not be dismantled without destruction and damage to the seed crystal, which greatly restricts the frequent use of the seed crystal and / or its holder.

According to the state of the art, in the growth of single crystals of melts, melt solutions and solutions with moving seed crystal, the following stabilization methods are usually used for the automatic control and regulation of the crystal growth process, which differ with respect to the physical nature of the controlled technological parameter and its metrological realization:

1. Temperature measurement directly in the crystallization zone by means of a thermocouple positioned there;

2. Control of crucible temperature;

3. Optical scanning of the growing crystal by means of a television system;

4. imaging the growing crystal with X-rays or gamma rays;

5. Pyrometric monitoring of the meniscal area;

6. Meniscus control by means of active optical methods;

7. Measurement of melt level reduction in the crucible;

8. Gravimetric crystal diameter control (weight method).

From "Journal of Materials Science" 11 (1976), p.259-263, the determination of the prevailing temperature in the crystallization zone by means of a near the interface in the melt positioned thermocouple is known, but the registered temperature profile only as an additional reading The disadvantage here is that the exact positioning of the thermocouple in the melt at a defined distance in front of the phase interface, which is required during the entire growing process, presents no difficulties as an actual value for the automatic control system based on another principle furthermore, that the temperature detector itself becomes a potential source of disturbance to the growth process and induces the presence of additional crystal defects by its presence, for example as a result of a change in the temperature profile and a thermocouple disturbance of the convection tion behavior of the melt near the phase boundary. Finally, smelting impurities are due to undesired chemical reactions of the thermocouple material with the melt ("Journal of Scientific Instruments" 41 [1964], pp. 676-678], especially in high-temperature breeding ("Berichte der Deutschen Keramischen Gesellschaft" [1963], p. 615-619), can not be ruled out.

Another stabilization method is based on the determination of the temperature of the crucible, the side or at the bottom thereof from the outside through the crucible embedding by means of thermocouples or pyrometrically ("Journal of Applied Physics" 31 [1960], p 1508, "Journal of Applied Physics "33 [1962], p. 1893;" Journal of the American Ceramic Society "45 [1962], pp. 474-478;" Improved Techniques for the Growth of Single Crystals Suitable for Laser Applications "Arthur D. Little Inc. [Dec 1965], pp. 1-37, US-PS 3865554; "Journal of Crystal Growth" 38 [1977], pp.206-212) .The control of the breeding process takes place via a control of the crucible temperature according to a predetermined program.

A disadvantage of this method is the fact that with increasing distance of the temperature measuring point of the crystallization zone (ie when using large crucibles to increase the achievable crystal dimensions) both a growing time shift between the occurrence of a temperature change before the interface and their metrological detection and a Decrease in the achievable detection sensitivity is recorded, whereby the control behavior of the respective stabilization system is deteriorated. This undesirable effect has an increasingly disturbing effect with increasing batch size, by making timely and in-phase influencing of the crystallization process difficult or even completely impossible since the measurement signal obtained also has a reduced signal-to-noise ratio and becomes worse and worse with increasing crucible dimensions Temperature response near the phase boundary correlates. Apart from systematic measurement errors that may occur in the pyrometric temperature determination of the targeted area of the outer wall of the crucible due to insufficient consideration of the spectral radiation properties of the crucible, shield and window materials used ("Applied Optics" 3 [1964], pp. 281-285; "Izlucatel'nye svoijstva tverych materialov - Spravocnik", Izd-vo Energiya, Moskva 1974 / russ.), When applying this method to stabilize the breeding process, it must be taken into account that, eg in the Czochralski method, the relation between the temperature profile measured on the crucible wall / bottom and the conditions prevailing near the crystallization zone (such as the shape of the melt isotherms, the magnitude of the axial and radial temperature gradients close to the growth front, etc.) ) can change considerably as the breeding process progresses. For this reason, the optimal course of the crucible temperature program required for producing regularly shaped single crystals of high quality has a relatively complicated shape. This temperature program must usually be for each type of crystal

according to the desired crystal size and breeding structure used sch rageweise empirically determined. Its course is very much dependent on the real starting conditions, such. B. from the crucible filling level, and reacts very sensitive to low tolerances of the breeding structure, whereby the reproducibility of the breeding process is significantly impaired.

Furthermore, optical control methods for scanning the growing single crystal by means of special television systems are used ("Journal of Crystal Growth" 13, 14 [1972], pp. 619-628; "Journal of the Electrochemical Society / Solid State Science and Technology" 120 [FIG. 1973], pp. 1272-1275; "Optik" 37 [1973], pp. 15-20; "Kristall und Technik" 8 [1973], pp. 1233-1242). In this case, the contrast between the image of the already grown crystal section and the area of the melt meniscus is exploited. When using a suitable electronic evaluation of the video signal obtained is - depending on the substance-specific radiation and transmission properties of the crystals grown and their melts - in certain cases, a relative measurement of the temperature of near-surface regions of the melt and the growing single crystal possible. Because of the poor accessibility of the meniscus area z.T. Mirror systems used in the recipient, which fog during the breeding process, resulting in a strong reduction in the signal / noise ratio. A disadvantage in the application of this relatively complex stabilization method continues to be the fact that in comparison to other control methods larger crucibles must be used to keep the deterioration of visibility by the decrease in the melting level in the crucible with progressive growth process in limits. As a particularly serious technical and economic disadvantage, this is especially important in high-temperature breeding, since especially at high operating temperatures in order to prevent harmful reactions of the melt with the material of the crucible, this often must consist of the costly and difficult to process iridium.

In another method for automatic growth control of the melt pulled single crystals of the already grown crystal section immediately above the meniscus area of a laterally incident, collimated, the crucible and crucible wall crucible penetrating penetrating X-radiation, their spatial intensity distribution after passing through the hot zone with a suitable radiation detector (eg, Geiger or scintillation counter or display on a fluorescent screen) is evaluated, which is arranged at the same height as the radiation source on the opposite side of the breeding structure (Nederlands Patent 6512921, US-PS 3499736, GB-PS 1154240; Journal of Crystal Growth "3,4 (1968), pp. 286-290;" Acta Electronica "17 (1974), pp. 45-55;" Journal of the Electrochemical Society "121 (1974), pp. 822-826 "Journal of Crystal Growth" 21 (1974), pp. 310-312; "Journal of Crystal Growth" 40 (1977), pp . 1-12), and Gamm Radiation sources are used in this method ("Pribory i sistemy upravlenija'Vruss. 1967, No.2, p.4-6). Increasing the contrast of imaging the growing crystal usually requires additional filters in the beam path, while a special crucible lifting mechanism compensates for the melt level reduction during the growing process. The error signal obtained by this method is proportional to the deviation of the current value of the crystal diameter from the target value. A particular disadvantage is the limited practical applicability of this stabilization method, which can be used only in the production of such media in which the required crucible material for the relevant type of radiation is sufficiently permeable and the growing single crystal simultaneously has a sufficiently high absorption capacity for this radiation, thus a for the signal evaluation sufficient contrast of the shadow image of the monitored meniscus area from the environment can be achieved. These conditions are usually met in the growth of semiconductor crystals from non-metallic crucibles, but not in the production of single crystals of high-melting oxidic compounds, the z. B. for use in laser technology are of great importance. Finally, for the safe application of this stabilization method, additional appropriate radiation protection measures must be ensured. Also known is the detection of radiation emanating from the meniscus area, for which purpose it is targeted by means of special optical systems from obliquely upwards through corresponding openings in the thermal shielding of the breeding structure (DE-OS 1 619954, DE-AS 1 619 967, US-PS 3337303; US-PS 3493770; DE-OS 2143553; "DENKI KAGAKU" 40 [1972], p. 521) shows the radiation emanating from the meniscus area itself or the fraction of the heat from the inside of the crucible on the meniscal surface in the detector direction outgoing radiation ("Journal of Crystal Growth" 29 [1975], p. 326-328) is measured pyrometrically and analyzed the radial / azimuthal intensity distribution. Although this method has proved to be advantageous for controlling the crystallization process, in particular in the growth of semiconductor single crystals ("Semiconductor Products and Solid State Technology" October 1970, pp. 25-30; "Solid State Technology", October 1971, p -45, 58; "DENKI KAGAKU" 40 (1972), p.521; "Solid State Technology", February 1974, pp.33-36, 55), however, the measured values thus obtained are not unaffected by the breeding atmosphere. Since the meniscus area must be targeted from the outside, injuries of the thermal symmetry in the crystallization zone as well as a visual deterioration with progressive breeding process due to melt level reduction and fogging on the optical systems used can not be completely ruled out. An immediate metrological accessibility of the crystallization front is not given in this method, but it is based on the targeted utilization of the material-specific (semiconductor!) Strong change in the angle of maximum radiation emission even with a slight change in the meniscus shape. Another problem is the considerable uncertainty of Meßsignalauswertung in the growth control of crystals that have no rotationally symmetrical shape, which is often the case with wax-oriented single crystals.

According to the state of the art methods of meniscus shape monitoring by means of active optical methods are also used (US-PS 3291 650, "Journal of Crystal Growth" 15 [1972], pp. 85-88; "International Electronic Review" 1974, no. P.91-94; "Acta Electronica" 17 (1974), pp. 45-55), in which a bundled light beam is directed from the outside to a suitable meniscus area, wherein a laser is advantageously used as the external radiation source By means of reflected radiation, in particular from the size of the reflection angle, process-relevant information on the dynamics of the growth process can be derived, which are in principle suitable for the automatic control of the growing process, because crystallography according to the Czochralski method has a clear relationship between the diameter the growing crystal in the meniscus area and the forming form of the enamel surface ( Journal of Crystal Growth "15 [1972], pp 85-88). Although this active method is compared to the above-mentioned passive methods of pyrometric meniscus monitoring less dependent on the substance-specific emission properties of the respective melt / melt solution, but is otherwise subject in principle with the same disadvantages that are all comparable optical control methods in which the measuring channel laterally of the drawing axis or obliquely through the thermal shielding components of the crucible construction and / or is affected by the breeding atmosphere.

Another method for controlling the crystal growth process is based on indirectly determining the mass growth rate by measuring the change over time of the melt volume. Known metrological variants of this integral method, the melt volume determination on a measurement of melt level reduction during the breeding process back. This detection takes place z. B. taking advantage of the electrical conductivity of melt and crucible on the alternate closure and opening of an electrical circuit by a laterally growing monocrystal intermittently from above into the melt immersed metallic electrode, each during the immersion process, the vertical position of the contact electrode upon contact of the melt level is used as criterion for the current melt level (Perner, Stransky "Some peculiarities of the automation of the growing process of ruby red crystals" /russ./ - Theses of the 2nd RGW symposium on automation of the crystal growing process, Prague, 29.11.1978) According to this method, the non - excludable enamel contamination by the electrode material as well as the symmetry of the temperature field in the hot zone of the growth structure, disturbed by the electrode, limits the practically unavoidable electrode corrosion theoretically possible high accuracy of measurement of this integral measuring method, in its application, however, no direct information about the shape of the crystallization front are obtained. Another variant for determining the melt level reduction is based on the evaluation of the change in the electrical resistance of the already grown crystal and the wall of the crucible located melt (DE-OS 2635093). Since the measuring circuit is formed by the series connection of the electrical resistances of seed crystal, already grown crystal section and the remaining melt, so that the applicability of this method is practically limited to the cultivation of semiconductor single crystals. According to the prior art, a contactless interferometric measurement of the melt level reduction is known in which the distance between a beam splitter and the melt surface is part of a Michelson two-beam interferometer (DE-AS 2337169). The melt reduction is measured in units of the wavelength of light used and used to control the drawing parameters. The light source is a laser. A disadvantage of this arrangement, especially their high sensitivity to virtually always existing vibrations of the breeding apparatus and caused by convection local movements of the enamel surface, which requires at least a very complex signal evaluation.

A likewise known method for stabilizing the crystal growth process is based on the gravimetric crystal diameter control (weight method). In this case, the time profile of the weight of the growing crystal and / or the melt including the melt meniscus area is detected by means of one or more weight detectors. The common variants of this method differ with regard to the type of detector arrangement:

a) registration of the weight of the growing crystal, wherein the weight detector is located on or in the drawing spindle (US Pat. No. 2908004, DE-AS 1245317, DE-OS 1 519 898, "Journal of Materials Science" 2 (1967, p. 299; "Journal of Crystal Growth", 3,4 (1968), pp. 471-474; DE-A-2,208,758; "Journal of Crystal Growth", 13, 14 (1972), pp. 555-559; "Journal of Crystal Growth "16 (1972), pp. 277-279," Transactions of the Society of Instrument and Control Engineers "Japan (1973), pp. 595-600, DE-OS 2345048, USP 39349832;" Journal of Crystal Growth "; 21 (1974), pp. 283-286; GB-PS 1478192; DE-OS 2446293; "Pribory isistemy upravlenija" / russ. (1975) No. 5, pp. 7-9; "Journal of Crystal Growth" 29 (British Pat. Journal of Crystal Growth 40 (1977), pp. 13-28; "Journal of Crystal Growth" 42 (1977), pp. 473-482; Senff, I., Arsenev, PA: Lecture Thesis II. RGW-Kristallzucht-Automatisierungskolloquium, Prague, 29.11.1978);

b) recording the time course of the weight of the melt contained in the crucible, wherein the weight detector is arranged below the crucible structure inside or outside the recipient (US-PS 2908004, US-PS 3259467, DE-OS 1519898, "Journal of Crystal Growth" 19 (1973), pp. 187-192; "Materials Research Bulletin" 8 (1973), pp. 443-450; "Bell Laboratories Record" 51 (1973) p. 30; "Transactions of the Society of Instrument and Control Engineers 'V Japan (1973),

Pp. 595-600; "Acta Electronica" 17 (1974), pp. 45-55; British Patent 1,465,191; "Journal of Crystal Growth" 24, 25 (1974), pp. 369-373, 432-436; "Journal of Crystal Growth" 26 (1974), pages 1-5; "Materials Research Bulletin" 10 (1975), pp. 9-14,701-707; DE-OS 2513923; CH-PS 580805; "FUJITSU Scientific and Technical Journal" / Japan 12 (1976) No. 1, pp. 93-113; "Journal of Crystal Growth" 38 (1977), pp. 206-212; "Journal of Crystal Growth" 40 (1977), pp. 13-28; "Journal of Crystal Growth" 41 (1977), pp. 262-274; "Journal of Crystal Growth" 42 (1977), pp. 473-482; Preprint FlAN No. 148, Moskva, 28.7.1978; KFKI Report 1979-16, Budapest 1979).

There are also differences in the structural design of the force measuring element, in the measurement signal processing (analog / digital) as well as in the controlled controlled variable (absolute-i.e., integral-weight value or mass growth rate as its time derivative).

After appropriate signal evaluation, suitable control signals are formed on the basis of the respectively current value of the weight and / or the mass growth rate, which is used in this method as parameters relevant for the actual course of the crystallization process, which control processes of the crystal growing apparatus control the breeding process in the Meaning of an automatic stabilization of growth conditions.

Despite numerous application advantages of this method, when used alone, no direct information on the shape and dynamics of the crystallization front is obtained. Since the weight value obtained is derived from an integral measurand, the amount of which necessarily reflects the real growth process only if the shape of the crystallizational front remains virtually unchanged during the advancing crystal growth process, the sole application of the gravimetric crystal diameter control leads to unsatisfactory results in practice if in the course of the breeding process - eg due to hydrodynamic interaction in the melt, flow induced phase boundary instabilities occur. The latter can not be recognized as such by a control system based solely on a gravimetric basis, at least in time, and lead to a misinterpretation of the actual course of the crystallization process by the stabilization system and thus to erroneous adjustments with all the associated negative effects on the crystal perfection. This fundamental lack of the weight method occurs particularly clearly when an interface envelope occurs during the cultivation process, which manifests itself macroscopically as an abrupt change in diameter of the growing crystal with the associated disruptions of the real structure ("Materials Research Bulletin" 10 [1975] pp. 701-707 , "Journal of Materials Science" 11 [1976] pp. 259-263, "Journal of Crystal Growth" 32 [1976] pp. 89-94, "Materials Research Bulletin" 13 [1978] pp. 675-680).

Object of the invention

It is an object of the invention to eliminate the disadvantages and deficiencies of the prior art described, to objectify the crystallization process in the crystal growth of melts, melt solutions and moving seed crystal solutions as far as possible and to automate the breeding process, to increase the quality of the crystals produced Increase labor productivity and thus improve the overall economy of the growth process in the production of single crystals.

Explanation of the essence of the invention

The invention is based on the object in plants for the growth of single crystals of melts, melt solutions or solutions with moving seed crystal by special design and dimensioning of a germ bar holder and associated with Impfkeimstange, especially by avoiding a "hot" junction between seed crystal and seed holder, a Possibility for the stable and reproducible attachment of a replaceable seed crystal rod to the pulling spindle of the growing apparatus and to obtain during the growing process the immediate crystallization process on the growth front (interface) as well as further process-relevant parameters characterizing and evaluable data and measurands, for automatically controlling the crystal growth process, including the application of adaptive control systems.

According to the invention, this object is achieved in an arrangement for determining the crystallization process characterizing data and / or measured quantities in plants for crystal growth of melts, melt solutions or solutions with a rotating and axially movable pulling spindle with germ bar holder characterized in that a seed crystal of a defined crystallographic orientation representing, regardless provided by the speed of the adjusted drawing spindle and the working temperature stable, reproducible and easily replaceable, monocrystalline Impfkeimstange of high optical quality is that inside the Keimstangenhalters or the drawing spindle, preferably in the axis thereof, at least one of the crystallization zone and its immediate vicinity outgoing thermal radiation and through them, originating from the melt volume and areas of the crucible inner wall background radiation detecting radiation receiver and / or For external radiation of a preferably arranged in the Keimstangenhalter or in the drawing spindle thermal or non-thermal optical radiation source on the growth front and directed by this reflected radiation on these radiation receiver conductive optical elements and aperture and filter arrangements are provided that preferably at least one additional, one or more more , the current state of the crystallization process characterizing parameter measuring detector is disposed inside the germ bar holder or the drawing spindle.

That the seedbed comprises at least one undoped and doped region along its longitudinal extent, the doped region having both heat radiation absorbing properties for at least one spectral range adapted to the spectrum of the spectral region dependent on the absolute temperature of the crystallization zone and the radiation maximum corresponding to that temperature; suitable spectral ranges represents a selective radiation conductor.

It is particularly advantageous for the purpose of preventing undesired contamination of the melt by the doping elements contained in the doped region of the Impfkeimstange that the doped region in the germ bar holder adjacent - d. H. the melt facing away - part of Impfkeimstange is provided. In order to achieve the desired absorption behavior of the monocrystalline Impfkeimstange it is desirable that their doped region contains as doping ions of at least one of the elements dysprosium, holmium, erbium or thulium.

For the determination of measurement variables characterizing the crystallization process, it is advantageous, in particular in high-temperature cultivation, for the doped region of the seed nucleus to be radiation-transmissive in narrow-band spectral ranges suitable for color temperature measurements (quotient pyrometers), preferably in the range from 1000 to 3000 nm.

Especially in the sense of largely preventing the heat removal from the crystallization zone through the Impfkeimstange inside the Keimstangenhalters, it is expedient that the doping concentration depending on the length of the doped region and of the effective for the incorporation of the respective ions distribution coefficient 2 to 20 mol. % and that on the Impfkeimstange heat-shielding and / or heat dissipating elements are provided. The registration of the background radiation emanating from the melting zone and regions of the crucible inner wall during the growing process from the crystallization zone and its immediate surroundings and by means of a pyrometer arrangement based on the partial radiation measuring principle is advantageously achieved by having only one radiation detector in the axis of the Keymstangenhalters or the pulling spindle is arranged and that is located between this radiation detector and the Impfkeimstange a narrow-band interference filter whose nominal spectral transmittance maximum is tuned to one, influenced by the doping elements used spectral region in which the doped Impfkeimstange represents a selective radiation splitter, the narrow-band interference filter In the beam path, a broadband order filter may be additionally connected upstream.

A further improvement of the achievable temperature resolution while reducing the distorting influence of Drifterscheinungen, caused in particular by not completely excludable thermal influences on the radiation detectors used, is advantageously achieved in that are preferably used as radiation receiver Si photoelements in a ratio pyrometer (quotient pyrometer) at the determined temperature values are determined from the ratio of the radiation densities in at least two spectral ranges. Advantageously, only a single radiation receiver is used in the ratio pyrometer arrangement, which is fixedly arranged in the measuring beam path and the narrowband spectral ranges determined by the absorption behavior of the rare earth ions present in the doped region of the seed germinal rod from the crystallization zone through the growing crystal and the seed germ rod in suitable color temperature measurements exposure to radiation is exposed in an alternating sequence. According to the invention this is achieved in that between the Impfkeimstange and located in the axis of the Keimstangenhalters or the drawing spindle radiation detectors driven by the drawing spindle, disposed in a direction perpendicular to the spindle axis Rotärealnterferenzfilter with at least two sectors of different spectral transmittance, wherein the axis of rotation of Filters is parallel to the Ziehspindelachse that these filter sectors are arranged to each other so that they are turned on in the course of one revolution of the filter in succession in the Meßstrahlengang that the rotating sector-shaped interference filter in the beam path, a broadband order filter may be additionally upstream and that a brand transmitter is provided which then always emits a trigger pulse to a downstream evaluation unit if one is located on the bisector of the azimuthal opening angle of a filter sector s area of the rotating interference filter passes through the Meßstrahlengang.

The realization of the high-resolution and drift-poor ratio pyrometer principle, in which only one radiation receiver is exposed alternately in at least two different, narrow-band spectral regions of the temperature radiation to be detected, can be achieved according to the invention advantageously characterized in that between the Impfkeimstange and in the axis of the Keimstangenhalters or the drawing spindle located radiation detectors driven by the drawing spindle, in a plane perpendicular to the spindle axis plane, known per se, gradient interference filter is arranged, wherein the axis of rotation of the gradient interference filter extends at an adjustable distance a from the Ziehspindelachse, and that a Brand transmitter is provided, which always emits a trigger pulse to a downstream evaluation unit when the respective filtered through the filter area depending on the set distance a reachable Wavelength extreme (X _min or A _max ) corresponds.

A significant advantage of this measuring arrangement is that for the practical realization of a sequential spectral filtering of the reaching of the crystallization from the radiation detector temperature radiation - in contrast to the use of a specially designed for the intended use with high effort sector-shaped interference filter - a commercial gradient interference filter (VIF) can be used. This VIF requires no subsequent mechanical processing, which is in view of its required long life and temporal consistency of the optical properties of crucial importance.

Taking into account the breeding conditions which change as the growth process progresses, the arrangement according to the invention makes it possible simultaneously to obtain measured values which are derived from the growth process influencing and / or characterizing parameters of different physical nature and which, according to suitable sig., Are obtained via at least two different measuring channels during the growing process 'Nalbehandlung and evaluation, preferably involving correlation techniques, as process-relevant input variables for a more advanced, multi-channel control system with adaptive control behavior are suitable, its use in crystal growing systems, expediently involving a process computer, an automatic optimization of crystal growth conditions over the entire course of the breeding process allows. The application of automatically optimizing control and regulation algorithms for monitoring and targeted influencing of the crystallization process is an essential prerequisite for the growth of single crystals of high perfection. This object is achieved by means of the described arrangement in that at a sufficiently protected from thermal stress, chemical influences of the breeding atmosphere and electromagnetic interference in the interior of the germ bar or the pulling spindle at least one other than to register thermal and / or non-thermal optical radiation (Laser) detector of suitable constructive design is mounted so as to allow unimpeded simultaneous registration of the time course of the values of at least two different parameters characterizing the current state of the crystallisation process, i. H. in spite of the spatially adjacent arrangement of the different detectors, there is no disruptive mutual influencing of the measured values obtained in the various measuring channels due to the measuring principle. Particularly meaningful, the current

Measurements characterizing the course of the crystallization process are obtained, in particular, when the other detector used for registering thermal and / or non-thermal optical radiation is a weight detector. By applying the invention, the fulfillment of an easy-to-handle, frequently reusable, seed crystal seedling germ, which has hitherto met only unsatisfactorily in high-temperature breeding (HTZ) of monocrystals, is achieved by the precise, stable and reproducible position of the defined crystallographic oriented seed crystal is guaranteed regardless of the speed of the pulling spindle and the working temperature.

In fulfillment of this requirement allows the arrangement according to the invention, in the event of unforeseen solidification of the melt, caused z. B. by disturbances in the power grid or sudden defects in the heating energy source of the crystal growing apparatus to prevent the breakage of Impfkeimstange or already grown on her single crystal parts of the arranged between pulling spindle and Impfkeimstange Keimstangenhalters in terms of a torque-dependent "slip clutch" and thereby due to their sufficiently large distance from the hot crystallization zone as well as the strong heat absorbing effect of the doped region of the monocrystalline seed in combination with those on it attached heat-shielding and / or heat-dissipating elements are slipping clutch and Einspannstelle the Impfkeimstange in a sufficiently cool area in the vicinity of the usual water-cooled drawing spindle, so that at this point conventional chucks and ordinary slip clutch designs are applicable. To protect the arranged in Keimstangenhalter sensitive detectors in front of the output of the hot zone thermal energy dependent on the respective operating temperature minimum distance between them and the crystallization zone is necessary, which requires a relatively large length of Impfkeimstange-especially in the HTZ. At the same time, their embodiment according to the invention as a consistently monocrystalline seed germ cage counteracts the requirement for adequate mechanical stability. However, their absolute value is not only dependent on the real structure, but is also limited by material-specific properties, which must be taken into account in the concrete practical application case. The operational advantages of the described monocrystalline Impfkeimstange are especially at high working (dhKristallisations-) temperatures evident, although their applicability is also given in the crystal growth of melt solutions / solutions, which generally takes place in lower absolute temperature ranges. Particularly positive is the elimination of a thermally highly stressed, serving as an extension piece, not monocrystalline component (eg., A ceramic rod or a tube above) between actual seed crystal and the attachment point on the pulling spindle and thus avoiding a thermally heavily loaded and therefore critical juncture between the seed crystal and a commonly used, non-single crystalline extension, since in HTZ there is usually undesirable and barely reproducible distortion of this non-single crystal component during the heating phase and later in the growing process, despite careful adjustment prior to start of growth - d , H. in a cold state-to uncontrolled and unwanted-wsii'ka. damaging misalignments of the position of the seed crystal with respect to the predetermined by the axis of the pulling spindle pulling direction in the hot operating state leads. The use of the monocrystalline seed bar of high optical quality and good mechanical stability in the inventive arrangement allows its use as part of a measuring channel in the optical (including infrared) range of electromagnetic radiation. Depending on the type and concentration of doping and the longitudinal extent of the seeded germinal rod, it acts as a selective optical fiber for certain relatively narrow spectral regions of the spectrum of the spectrum emanating from and passing through the crystallization zone and its immediate surroundings during the growth process, from the melt volume and interior crucible wall regions originating background radiation. Thus, the entire measuring channel in the optical region consists of an arrangement which is formed from the growing crystal itself and the Impfkeimstange invention. In conjunction with their positive and non-positive attachment to the germ bar holder, the seed bar used simultaneously acts as a hermetic seal between the sensitive detector arrangements housed in the germ bar holder and the often aggressive breeding atmosphere. The latter, especially in the HTZ, in the vicinity of the hot zone of the breeding structure, is usually enriched with evaporating constituents of the melt, the crucible embedding material and volatile products of the thermal dissociation of the melt. If necessary, z. B. from constructive requirements, this optical measuring channel can be extended without adverse effects on the measurement still to a between the the drawing spindle facing end face of the Impfkeimstange and the particular radiation detector used interstice, in which as a characteristic feature of a maintained in the recipient of the breeding apparatus breeding atmosphere (including Vacuum) hermetically sealed, non-measuring atmosphere prevails (eg inert gas or air) or is filled by another, transparent in the optical range medium.

Finally, taking advantage of the above-mentioned features of the optical measuring channel by the use of a preferably in Keimstangenhalter, in the drawing spindle or its axial extension arranged thermal or non-thermal optical radiation source can be a direct experimental access in-situ control of the spatial course and temporal changes Interface form whose behavior is essential for the progress of the crystallization process and which - in particular in the high-temperature crystal growth according to the Czochralski method - a comparable on-line control by conventional methods is not accessible.

According to the invention, the control of the interface behavior and - based on the information obtained in the real time scale - their targeted influencing realized by an active method of optical localization of the growth front is applied by passing through the optical measuring channel on defined areas of the phase interface between the directed crystal and its melt / melt solution, a focused beam of light and reflected at the interface, received by the optical measuring channel to the radiation receiver zurückgelangende part of this measuring light as a useful signal and its temporal and spatial intensity distribution is evaluated in a suitable manner. Expediently, a LASER is used as a source of extraneous radiation, the characteristic high spectral radiance of which is particularly advantageous in that, in the signal evaluation, the separation of the relatively weak useful signal from the interfering thermal background radiation is supported by the use of narrow-band spectral filtering.

-TU-

With this arrangement, a high-resolution, interferometric measuring method for detecting the dynamic behavior of the interface during the growth process can be realized advantageously in which the existing optical measuring channel from the already grown crystal portion and the invention monocrystalline, partially doped seed germination rod high optical quality part of a Michelson interferometer arrangement represents. Finally, in addition to statements about the form and temporal behavior of the interface, further information can be derived from the character of the measurement signal which is obtained in this active method for the optical localization of the growth front using the monocrystalline seed germ cage according to the invention. This concerns above all the possibility of an early detection of the occurrence of inclusions, such. As of Tiegelmaterialpartikeln, gas bubbles or other foreign phases in the growing single crystal whose presence in the crystal usually excludes its suitability for the intended use and thus brings considerable economic losses. The occurrence of said inclusions can be caused by very different causes, eg. B. by constitutional supercooling, stoichiometric deviations or uncontrolled impurities of the charge used, reaction of the melt with the crucible material and / or the culture atmosphere, thermal dissociation processes in the hot zone with subsequent sublimation of the volatile components, chemical transport reactions, bubble or particle capture by a rough Growth front and a. m., so that in the practice of crystal growth such phenomena can not be completely ruled out despite careful trial preparation and implementation. It is therefore of great economic importance, especially during the production of doped dielectric single crystals for use as an active laser medium usually necessary long breeding times to obtain already during the breeding process knowledge of the occurrence of such phenomena, either to take countermeasures can (z B. by stopping the growth process and continuing the breeding process after the melt back of a part of the already grown single crystal and taking appropriate precautions against the repeated occurrence of these inclusions), or at least cancel the breeding process reasonably, so that the respective crystal growing plant as soon as possible for the next breeding can be used.

By the application of the invention it is possible to obtain simultaneously via different measuring channels such measured values which are relevant for processes which take place directly in the region of the crystallization zone as well as in the region of the melt meniscus surrounding the growing crystal.

It is essential that, in contrast to comparable known measurement methods, the registration of these signals is not affected or distorted by disturbing effects of the breeding atmosphere, which is in other optical control methods, eg. B. due to turbulence phenomena of the breeding atmosphere and uncontrollable changes in the optical properties of usually arranged inside the recipient of the breeding apparatus viewing windows, Strahlumlenkspiegeln or other optical components by increasing fogging, discoloration o. Ä. With progressive breeding process, in principle can not be excluded.

A significant advantage for the practical use of the arrangement described is further that the necessary to achieve the working temperature with simultaneous realization of small temperature gradients - especially in the HTZ - all-round thermal shielding of the hot zone for the application of the listed combined measurement methods is not limiting ,

Occurring irregularities during the crystallization process can be detected by evaluating the data obtained over several measurement channels time and with higher security than in the known methods and thus harmful effects on the achievable crystal perfection by timely and appropriate influencing the control of the breeding process can be avoided.

The feasible with the inventive arrangement multi-channel process monitoring, characterized by continuous registration of prevailing in the immediate vicinity of the crystallization temperature conditions by a pyrometric method while tracking the shape and dynamics of the growth front by means of an active method of optical localization of the interface including simultaneous determination of the current value of the integral mass growth rate using a weight detector, ie The determination of the mass crystallized per unit time, in particular for the control of flow phenomena of great practical importance, since the latter provide a significant contribution to the thermal energy balance at the interface and thus significantly influence their behavior. So z. B. the occurrence of convective instabilities in the course of the breeding process, the per se universal applicability of the widespread in the Czochralski crystal growing crystal diameter control by weight method often limited.

The transition to the described multichannel process monitoring and control is particularly advantageous because it has been found in practice that the use of a merely "single-channel" automatic stabilization method to control the crystal growing process is in many cases not sufficient to produce single crystals of high structural perfection Thus, in addition to the known measures for controlling the crystallization process, including the use of automatic crystal growth stabilization devices, for example, the control of heating power, lifting and rotational speed and their combined temporal variation for the purpose of deliberately influencing the interface shape count, as a necessary prerequisite for an achievable high crystal quality is always a targeted optimization of the breeding structure used for the cultivation of a specific crystal type, its suitable design (eg., Geometry of enamel crucible and reheater, their mutual distance and their relative position within a high-frequency inductor or resistance heater, execution of the crucible embedding and other thermal shielding elements and the size and arrangement of the usually present in them vents, formation of the gas guide in the hot zone, etc.) the for the crystallization process essential value of the axial and radial temperature gradients in the melt, in the region of the crystallization zone and in the growing crystal as well as ensuring stable convection conditions in the crucible during the entire duration of the crystallization process depend critically. The described multichannel measuring arrangement, with suitable signal evaluation of the measured values registered in the various channels, allows the earliest possible and reliable detection of the occurrence of hydrodynamically induced convection instabilities, even before their manifestation and consequently the occurrence of significant instability of the growth front or even its envelope.

In addition, the arrangement of the invention provides in contrast to known solutions in addition to process-related control signals for an automatic system mitadaptivem control behavior to stabilize the crystal growing process additionally objective criteria for the assessment of the quality of each used Breeding Aufauf construction. While the conventional manner, the gradual optimization of the breeding structure is carried out on a more or less empirical basis, when using the described measuring arrangement as an objective yardstick for the suitability of each tested breeding structure for the specific breeding task and its comparison with other constructions expediently time and frequency of occurrence of Flow or growth instabilities during the breeding process and / or amount and direction of the changes made to their suppression or elimination by the automatic stabilization system of certain breeding parameters, such. B. the heating power and / or the crystal rotation speed, are used. This objectification of the development process reduces the development time, serves to increase the crystal quality and to improve the achievable in the standard crystal production process reproducibility and thus makes a total contribution to the further development of advanced crystal growing technologies, especially in the field of particularly problematic high temperature breeding.

embodiment

The invention will be explained in more detail below by exemplary embodiments. In the accompanying drawing show

1 shows schematically a crystal growing apparatus,

2 shows schematically a specially trained Impfkeimstange,

3 shows a typical absorption spectrum of Dy ³⁺ in a garnet host lattice,

4 shows a typical absorption spectrum of Ho ³⁺ in a garnet host lattice,

5 shows a typical absorption spectrum of Er ³⁺ in a garnet host lattice,

6 shows a typical absorption spectrum of Tm ³⁺ in a garnet host lattice,

7 shows the spectral radiance of a blackbody at T = 2250K,

FIG. 8 shows the radiation component of a black 2250K radiator transmitted by YAG: Dy ^3+. FIG.

9 shows the top view of a sector-shaped interference filter arrangement,

10: the top view of a gradient interference filter arrangement with associated typical signal waveform.

The part of a crystal growing apparatus shown schematically in FIG. 1 comprises a hermetically sealed recipient 1, in which within a thermal shield 2 a crucible 4, which can be heated by a heating device 3, is located with the melt 5. In the upper part of the recipient 1, a hermetic passage 6 is arranged, in which a cooled drawing spindle 7 is mounted rotatably and axially displaceable, which is offset by non-illustrated drive members during the crystal growing process in a combined translational / rotational movement. At the melt 5 facing end side of the pulling spindle 7, a hollow trained Keimstangenhalter 8 is disposed in the interior of the recipient 1, which has a fixing unit 9 for a Impfkeimstange 10. The fixing unit 9 comprises a chuck 11, a slip clutch 12 and a detector receptacle 13 and ensures a secure mounting of the mitwärmeabschirmenden / -abführenden elements 14 provided Impfkeimstange 10, at the melt 5 facing endesich is drawn from the melt 5 monocrystal. Preferably within the germ bar holder 8 are one or more radiation receivers 16 and optionally an optical radiation source 17, e.g. a laser, as well as radiation-conducting optical elements 18 are arranged which on the one hand emanating from the crystallization front 19 and its immediate environment, the already grown part of the single crystal 15 and the Impfkeimstange 10 continuous diffuse radiation through aperture 20 and filter assemblies 21 to the radiation receivers 16 and on the other the bundled extraneous radiation emanating from the optical radiation source 17 passes through the Impfkeimstange 10 and the already grown part of the single crystal 15 to the crystallization front (phase interface) 19 and the portion of the bundled extraneous radiation reflected by this back to the radiation receivers 16. In addition to the radiation receivers 16, a further detector 22 is arranged in the detector receptacle 13, which is suitable for registering other physical quantities than radiation, preferably for weight detection. The radiation receiver 16 and the additional detector 22 are connected via an evaluation device 23 with actuators 24 of the crystal growing apparatus for controlling the crystallization process influencing technological parameters, such as size of the heating power and lifting and rotating speed of the pulling spindle 7.

As shown in FIG. 2, the seed germ rod 10 used in the arrangement according to the invention is a crystallographically oriented and optically processed single-crystal cylindrical rod having along its longitudinal extent at least one undoped region 25 and one doped region 26 representing an absorption zone the undoped region 25 is located on the side of the Impfkeimstange 10 facing the melt 5 and preferably has the same chemical composition as the single crystal 15 to be grown. Between the undoped region 25 and the doped region 26 of the Impfkeimstange 10 is a production-related transition zone 27 along the longitudinal extent of the concentration of the dopant used for the doped region 26 doping material increases from zero to the value of the doped region 26 realized average doping concentration increases. Such a smooth transition of the degree of doping affects u.a. favorable to the mechanical stability and thermal resilience of Impfkeimstange 10 off. The doped region 26 is located on the side facing away from the melt 5 of Impfkeimstange 10, whereby impurities of the melt 5 with the dopants used in the doped region 26 dopants are avoided. This doped region 26 consists of the same host substance as the undoped region 25, but is additionally doped with certain rare earth ions, whereby it has heat radiation absorbing properties for at least one specific spectral range matched to the radiation maximum corresponding to the temperature prevailing in the crystallization zone 28. The effectiveness of the doped region 26 of the seed bar 10 as a thermal radiation absorption zone depends critically on the choice of doping elements and their concentration in this zone.

According to the invention, ions of the elements dysprosium, holmium, erbium or thulium - singly or in combination - are advantageously used as doping, in particular for the working temperature range of about 1800 K to 2500 K, which is important for high-temperature cultivation, the doping concentration being in a range of 2 to 20 mol%. lies. The deliberate introduction of ions of said rare earth elements in the doped region 26 also gives this the desired property of a selective radiation conductor in narrow-band spectral ranges suitable for color temperature measurements (quotient pyrometer) in the wavelength range of 1000 nm to 3000 nm. To illustrate this situation, FIG -6 the known ("Journal of Materials Science" 4 [1969] pp. 450-456) absorption spectra of the rare earth ions Dy ³⁺ , Ho ³⁺ , Er ³⁺ , and Tm ³⁺ in a garnet host lattice Spectra recorded at 300 K, they are to be regarded in qualitative terms for higher temperatures than representative, since at high temperatures above all caused by increased thermal lattice vibrations additional line broadening is to be expected and thus the absorption still increases the absorption behavior of the rare earth ions Dy ³⁺ , Ho ³⁺ , Er ³⁺ and Tm ³⁺ in the doped region 26 of Impfkeimstange 10 compared to the measuring thickness of 10 mm used in Fig. 3-6 a much greater absorption length of the order of 100-200 mm available needs in the present application of the doping to achieve the desired absorption effect, the absolute doping level in the doped region 26 of Impfkeimstange 10 for all practically significant dielectric host crystals only a few mol%, with no significant for the application deterioration of the crystal perfection (z. Strength reduction or inducing of refractive index inhomogeneities). Despite the lack of detailed knowledge of the spectral behavior of the optical measuring channel forming, semitransparent at the usually high operating temperatures materials Impfkeimstange 10 and the growing single crystal 15 can for qualitative estimates in a rough approximation for the spectral distribution of the melt 5 of a to be bred dielectric single crystal 15 through the crystallization front 19 in the direction of acting as the absorption zone doped region 26 of Impfkeimstange 10 total radiation (including the proportions of the background radiation) set the emission spectrum of a black body of the same temperature. With reference to FIG. 7, it becomes clear that the far predominant proportion of radiation in the wavelength range of 750 nm to 4000 nm lies in the working temperatures of 2,200 K which are usual for the growth of practically significant oxidic monocrystals (blackbody spectral radiance tables, VEB Deutscher Verlag der Wissenschaften, Berlin, 1972). Thus, dysprosium is preferably used for this area as a particularly advantageous doping element (FIG. 3). The high effectiveness of a Dy ³⁺ doping of Impfkeimstange 10 with respect to the achievable absorption of thermal radiation is illustrated by Fig. 8. In this figure, the dashed emission spectrum 29 of a blackbody radiator with the temperature 2250 K of the proportion of this black radiation transmitted by a dysprosium-aluminum garnet test sample used as a spectral filter with an absorption behavior according to FIG. 3 ("filtered" black radiation 30) The remaining maxima around 1100nm, 1500nm, 2100nm can be further reduced if necessary by a co-doping with preferably Hp ³⁺ (absorption maxima at 1200nm, 1900nm, 2100nm), Tm ³⁺ (absorption maxima at 1300nm , 1 800 nm) and / or Er ³⁺ (absorption maxima at 11.00 nm, 1600 nm) The doping ratio of Dy ³⁺ as main doping element to Ho ³⁺ , Tm ³⁺ and Er ³⁺ depends on the specific application Absorption zone acting, doped region 26 represents a germinal rod in the inoculation 10 integrated heat source which heats up in the breeding operation A clamped on the Impfkeimstange Combined radiation and cooling screen 31 supports the 'heat removal from the absorption zone. Except the top cooling plate 32, the horizontally disposed circular disc-shaped metal cooling plates 33-35 are blackened continuously on its upper side; On the other hand, all cooling plates are metallically bright and polished on the underside. The thermal energy dissipated from the cooling zone by the cooling screen is mainly radiated from the blackened surfaces. At the same time, the bare undersides of the cooling plates .32-35 form an effective shielding of the germ rod holder 8 against the heat radiation exiting the hot crucible 4 laterally adjacent to the seed rod 10 and, if not grown under vacuum, the upwardly directed hot gas convection currents , Advantageously, the cooling plates 32-35 slotted in the radial direction, whereby the inductive heating of the crucible, the unwanted energy coupling is kept low in the cooling plates. FIG. 9 schematically shows the arrangement for realizing the applied high-resolution and low-drift ratio pyrometer measuring principle, in which only one radiation receiver is exposed alternately in two different, narrow-band spectral regions of the temperature radiation to be detected. The sector-shaped interference filter 36 driven by the pulling spindle 7 rotates in a plane perpendicular to the spindle axis. It consists of two filter sectors 37 and 38 of different spectral transmittances, which face each other in pairs and, in the course of one revolution of the interference filter 36, are temporally successively pivoted into the measuring beam path. A brand transmitter 39 always emits a trigger pulse, not shown, when a region of the rotating interference filter 36 located on the bisector 40 of the azimuthal opening angle of a filter sector 37 or 38 passes through the measuring beam path. With this arrangement, an alternating spectral filtering of the radiation reaching the radiation receiver 16 through the measuring channel is realized in two narrowband spectral ranges. In a further embodiment variant, the high-resolution and drift-poor ratio pyrometer arrangement is advantageously realized by using a gradient interference filter 41 instead of the sector-shaped interference filter 36 (FIG. 10). The gradient interference filter 41 is disposed between the seed bar 10 and the radiation receiver 16 placed in the axis of the pull spindle 7, is driven by the pull spindle 7, and rotates in a plane perpendicular to the spindle axis. In this case, the axis of rotation 42 of the course interference filter 41 extends at an adjustable distance a from the drawing spindle axis 43. By varying the value of a, the wavelength difference Δλ = K _max - \ _mm swept over in the course of one revolution of the course interference filter 41 can be influenced and thus without Filter change are adapted to the specific application case, while by the choice of the value of Fig. 10, the desired wavelength centroid X _o = {X _max + A _m i _n ) / 2festgelegird. A brand transmitter 44 always emits a trigger pulse to an evaluation unit, not shown, if the respective filtered filter area corresponds to the wavelength extrema (K _mm or K _ma J achievable depending on the set distance a) Evaluation unit triggered, in each of which two laterally successive measured values KXmm), and l (X _max ) i is formed by means of a quotient circuit, not shown, corresponding to the in the i-th time interval at A _m j _n and A _max determined radiation intensity corresponding temperature value.

Claims (10)

1. An arrangement for determining the crystallization process characterizing data and / or measured quantities in plants for crystal growth of melts, melt solutions or solutions with moving seed crystal comprising a rotating during the crystal growing process and axially movable pulling spindle with Keimstangenhalter, characterized in that one, a seed crystal defined crystallographic orientation representing, regardless of the rotational speed of the aligned pulling spindle and the working temperature stable, reproducible and easily replaceable monocrystalline Impfkeimstang of high optical quality is provided that inside the Keimstangenhalters or the drawing spindle, preferably in the axis thereof, at least one of the crystallization zone and thermal radiation emanating from its immediate surroundings and background radiation passing through it and originating from the melt volume and regions of the crucible inner wall Radiation receiver and / or extraneous radiation of a preferably arranged in the Keimstangenhalter or in the drawing spindle thermal or non-thermal optical radiation source on the growth front-facing and reflected radiation from this radiation receiver conductive optical elements and aperture and filter arrangements are provided that preferably at least one additional, one or more further parameters measuring the parameter characterizing the current state of the crystallization process are arranged inside the rod holder or the drawing spindle such that the seed bar comprises at least one undoped and doped region along its longitudinal extent, the doped region having both heat radiation absorbing properties for at least one certain, depending on the spectrum of the absolute temperature of the crystallization zone and corresponding to this temperature maximum radiation ate spectral region and at the same time represents a selective radiation conductor in suitable spectral ranges. 2. Arrangement according to item 1, characterized in that the doped region is provided in the, the germ rod holder adjacent part of Impfkeimstangeund as doping ions of at least one of the elements dysprosium, holmium, erbium or thulium. 3. Arrangement according to item 1 and 2, characterized in that the doped region of Impfkeimstange in suitable for color temperature measurements (quotient pyrometer) narrow-band spectral ranges, preferably in the range of 1 000 nm to 3000 nm, is radiation-transmissive. 4. Arrangement according to items 1 and 2, characterized in that the doping concentration is 2 to 10 mol% depending on the length of the doped region and the effective for the incorporation of the respective ions distribution coefficient. 5. Arrangement according to item 1, characterized in that only one radiation detector in the axis of the Keimstangenhalters or the pulling spindle is arranged and that is located between this radiation detector and the Impfkeimstange a narrow-band interference filter whose nominal spectral transmission maximum on one, influenced by the doping elements used Is tuned spectral range in which the doped Impfkeimstange represents a selective radiation conductor, wherein the narrow-band interference filter in the beam path, a broadband order filter may be additionally connected upstream. 6. Arrangement according to item 1, characterized in that between the Impfkeimstange and located in the axis of the Keimstangenhalters or the drawing spindle radiation detectors driven by the pulling spindle, is arranged in a plane perpendicular to the spindle axis rotating interference filter with at least two sectors of different spectral transmittance , wherein the axis of rotation of the filter is parallel to the Ziehspindelachse that these filter sectors are arranged to each other so that they are turned on in the course of one revolution of the filter in succession in the Meßstrahlengang that the rotating sector-shaped interference filter in the beam path, a broadband order filter may be additionally upstream and that a brand transmitter is provided, which always emits a trigger pulse to a downstream evaluation unit, if one is on the bisector of the azimuthal opening angle of a filter sector Indisches area of the rotating interference filter passes through the Meßstrahlengang. 7. Arrangement according to item 1, characterized in that between the Impfkeimstange or located in the axis of the Keimstangenhalters or the drawing spindle radiation detectors driven by the pulling spindle, in a plane perpendicular to the spindle axis rotating, per se known, gradient interference filter is arranged , wherein the axis of rotation of the gradient interference filter extends at an adjustable distance a from the Ziehspindelachse, and that a brand transmitter is provided, which always emits a trigger pulse to a downstream evaluation if the respective irradiated filter area depending on the set distance a achievable wavelength extrema ( A _min or A _max ) corresponds. 8. Arrangement according to item 1 to 7, characterized in that preferably Si photosensitive elements are used as the radiation receiver. 9. Arrangement according to item 1, characterized in that heat-shielding and / or heat-dissipating elements are provided on the Impfkeimstange. 10. Arrangement according to item 1, characterized in that the other serving as a registration for thermal and / or non-thermal optical radiation detector is preferably a weight detector.